Platelet-activating factor plays a pivotal role in the induction of experimental lung injury

Characterization of Platelet Biologic Markers in the Early Pathogenesis of Postoperative Acute Respiratory Distress Syndrome

Animal models and limited human studies have suggested a plausible role for platelets in the pathogenesis and resolution of acute respiratory distress syndrome (ARDS). However, there are little data regarding the role of platelets in ARDS development.

OBJECTIVES

The objective of this study was to characterize the role of platelets in a postoperative ARDS model through an analysis of two platelet-specific biologic markers: thromboxane A₂ (TxA₂) and soluble CD-40-ligand (sCD40L).

DESIGN SETTING AND PARTICIPANTS

This was a nested case-control study of ARDS cases matched to non-ARDS controls. Blood samples were collected from a cohort of 500 patients undergoing thoracic, aortic vascular, or cardiac surgery that placed them at high-risk of developing postoperative ARDS.

MAIN OUTCOMES AND MEASURES

TxA₂ and sCD40L were analyzed at baseline (prior to surgical incision) as well as 2 hours and 6 hours after the key intraoperative events believed to be associated with increased risk of postoperative ARDS.

RESULTS

Of 500 patients enrolled, 20 ARDS cases were matched 1:2 to non-ARDS controls based on age, sex, surgical procedure, and surgical lung injury prediction score. Those who developed ARDS had longer surgeries, greater fluid administration, and higher peak inspiratory pressures. There were no significant differences in levels of TxA₂ or sCD40L at baseline, at 2 hours, or at 6 hours. There was also no difference in the change in biomarker concentration between baseline and 2 hours or baseline and 6 hours.

CONCLUSIONS

Two novel platelet-associated biologic markers (TxA₂ and sCD40L) were not elevated in patients who developed ARDS in a postoperative ARDS model. Although limited by the relatively small study size, these results do not support a clear role for platelets in the early pathogenesis of postoperative ARDS.

Reversible cross-tolerance to platelet-activating factor signaling by bacterial toxins

Bacterial toxins signaling through Toll-like receptors (TLRs) are implicated in the pathogenesis of many inflammatory diseases. Among the toxins, lipopolysaccharide (LPS) exerts its action via TLR-4 while lipoteichoic acid (LTA) and bacterial lipoproteins such as Braun lipoprotein (BLP) or its synthetic analogue Pam3CSK4 act through TLR-2. Part of the TLR mediated pathogenicity is believed to stem from endogenously biosynthesized platelet-activating factor (PAF)- a potent inflammatory phospholipid acting through PAF-receptor (PAF-R). However, the role of PAF in inflammatory diseases like endotoxemia is controversial. In order to test the direct contribution of PAF in TLR-mediated pathogenicity, we intraperitoneally injected PAF to Wistar albino mice in the presence or absence of bacterial toxins. Intraperitoneal injection of PAF (5 μg/mouse) causes sudden death of mice, that can be delayed by simultaneously or pre-treating the animals with high doses of bacterial toxins- a phenomenon known as endotoxin cross-tolerance. The bacterial toxins- induced tolerance to PAF can be reversed by increasing the concentration of PAF suggesting the reversibility of cross-tolerance. We did similar experiments using human platelets that express both canonical PAF-R and TLRs. Although bacterial toxins did not induce human platelet aggregation, they inhibited PAF-induced platelet aggregation in a reversible manner. Using rabbit platelets that are ultrasensitive to PAF, we found bacterial toxins (LPS and LTA) and Pam3CSK4 causing rabbit platelet aggregation via PAF-R dependent way. The physical interaction of PAF-R and bacterial toxins is also demonstrated in a human epidermal cell line having stable PAF-R expression. Thus, we suggest the possibility of direct physical interaction of bacterial toxins with PAF-R leading to cross-tolerance.

Bacterial lipoproteins in sepsis

Bacterial lipoproteins are membrane proteins derived from both gram-negative and gram-positive bacteria. They seem to have diverse functions not only on bacterial growth, but also play an important role in host's virulence. Bacterial lipoproteins exert their action on host immune cells via TLR2/1 or TLR2/6. Therefore, bacterial lipoproteins also need to be considered while addressing bacterial pathogenicity besides classical bacterial endotoxin like LPS and other microbial associated molecular patterns such as LTA, and peptidoglycans. In this mini-review, we provide an overview of general bacterial lipoprotein biosynthesis and the need to understand the lipoprotein-mediated pathogenicity in diseases like sepsis.

The Effects of Volatile Anesthetics on Lung Ischemia-Reperfusion Injury: Basic to Clinical Studies

Case reports from as early as the 1970s have shown that intravenous injection of even a small dose of volatile anesthetics result in fatal lung injury. Direct contact between volatile anesthetics and pulmonary vasculature triggers chemical damage in the vessel walls. A wide variety of factors are involved in lung ischemia-reperfusion injury (LIRI), such as pulmonary endothelial cells, alveolar epithelial cells, alveolar macrophages, neutrophils, mast cells, platelets, proinflammatory cytokines, and surfactant. With a constellation of factors involved, the assessment of the protective effect of volatile anesthetics in LIRI is difficult. Multiple animal studies have reported that with regards to LIRI, sevoflurane demonstrates an anti-inflammatory effect in immunocompetent cells and an anti-apoptotic effect on lung tissue. Scattered studies have dismissed a protective effect of desflurane against LIRI. While a single-center randomized controlled trial (RCT) found that volatile anesthetics including desflurane demonstrated a lung-protective effect in thoracic surgery, a multicenter RCT did not demonstrate a lung-protective effect of desflurane. LIRI is common in lung transplantation. One study, although limited due to its small sample size, found that the use of volatile anesthetics in organ procurement surgery involving "death by neurologic criteria" donors did not improve lung graft survival. Future studies on the protective effect of volatile anesthetics against LIRI must examine not only the mechanism of the protective effect but also differences in the effects of different types of volatile anesthetics, their optimal dosage, and the appropriateness of their use in the event of marked alveolar capillary barrier damage.

18F-fluoro-2-deoxyglucose PET informs neutrophil accumulation and activation in lipopolysaccharide-induced acute lung injury

INTRODUCTION

Molecular imaging of the earliest events related to the development of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) could facilitate therapeutic development and patient management. We previously reported that 18F-fluoro-2-deoxyglucose (18F-FDG) PET identifies ALI/ARDS prior to radiographic abnormalities. The purpose of this study was to establish the time courses of 18F-FDG uptake, edema and neutrophil recruitment in an endotoxin-induced acute lung injury model and to examine molecular events required for 14C-2DG uptake in activated neutrophils.

METHODS

Lung uptake of 18F-FDG was measured by PET in control male Sprague Dawley rats and at 2, 6 and 24h following the intraperitoneal injection of 10mg/kg LPS. Lung edema (attenuation) was measured by microCT. Neutrophil influx into the lungs was measured by myeloperoxidase assay. Control and activated human donor neutrophils were compared for uptake of 14C-2DG, transcription and content of hexokinase and GLUT isoforms and for hexokinase (HK) activity.

RESULTS

Significant uptake of 18F-FDG occurred by 2h following LPS, and progressively increased to 24h. Lung uptake of 18F-FDG preceded increased CT attenuation (lung edema). Myeloperoxidase activity in the lungs, supporting neutrophil influx, paralleled 18F-FDG uptake. Activation of isolated human neutrophils resulted in increased uptake of 14C-2DG, expression of GLUT 3 and GLUT 4 and expression and increased HK1 activity.

CONCLUSION

Systemic endotoxin-induced ALI results in very early and progressive uptake of 18F-FDG, parallels neutrophil accumulation and occurs earlier than lung injury edema. Activated neutrophils show increased uptake of 14C-2DG, expression of specific GLUT3, GLUT4 and HK1 protein and HK activity. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: 18F-FDG pulmonary uptake is an early biomarker of neutrophil recruitment in ALI and is associated with specific molecular events that mediate 14C-2DG uptake in activated neutrophils. 18F-FDG PET may provide a potential mechanism for early diagnosis and therapeutic assessment of ALI/ARDS.

Biosynthesis of oxidized lipid mediators via lipoprotein-associated phospholipase A2 hydrolysis of extracellular cardiolipin induces endothelial toxicity

We (66) have previously described an NSAID-insensitive intramitochondrial biosynthetic pathway involving oxidation of the polyunsaturated mitochondrial phospholipid, cardiolipin (CL), followed by hydrolysis [by calcium-independent mitochondrial calcium-independent phospholipase A2-γ (iPLA2γ)] of oxidized CL (CLox), leading to the formation of lysoCL and oxygenated octadecadienoic metabolites. We now describe a model system utilizing oxidative lipidomics/mass spectrometry and bioassays on cultured bovine pulmonary artery endothelial cells (BPAECs) to assess the impact of CLox that we show, in vivo, can be released to the extracellular space and may be hydrolyzed by lipoprotein-associated PLA2 (Lp-PLA2). Chemically oxidized liposomes containing bovine heart CL produced multiple oxygenated species. Addition of Lp-PLA2 hydrolyzed CLox and produced (oxygenated) monolysoCL and dilysoCL and oxidized octadecadienoic metabolites including 9- and 13-hydroxyoctadecadienoic (HODE) acids. CLox caused BPAEC necrosis that was exacerbated by Lp-PLA2 Lower doses of nonlethal CLox increased permeability of BPAEC monolayers. This effect was exacerbated by Lp-PLA2 and partially mimicked by authentic monolysoCL or 9- or 13-HODE. Control mice plasma contained virtually no detectable CLox; in contrast, 4 h after Pseudomonas aeruginosa (P. aeruginosa) infection, 34 ± 8 mol% (n = 6; P < 0.02) of circulating CL was oxidized. In addition, molar percentage of monolysoCL increased twofold after P. aeruginosa in a subgroup analyzed for these changes. Collectively, these studies suggest an important role for 1) oxidation of CL in proinflammatory environments and 2) possible hydrolysis of CLox in extracellular spaces producing lysoCL and oxidized octadecadienoic acid metabolites that may lead to impairment of pulmonary endothelial barrier function and necrosis.

Lipopolysaccharide Cross-Tolerance Delays Platelet-Activating Factor-Induced Sudden Death in Swiss Albino Mice: Involvement of Cyclooxygenase in Cross-Tolerance

Lipopolysaccharide (LPS) signaling through Toll-like receptor-4 (TLR-4) has been implicated in the pathogenesis of many infectious diseases. Some believe that TLR-mediated pathogenicity is due, in part, to the lipid pro-inflammatory mediator platelet-activating factor (PAF), but this has been questioned. To test the direct contribution of PAF in endotoxemia in murine models, we injected PAF intraperitoneally into Swiss albino mice in the presence and absence of LPS. PAF alone (5 μg/mouse) caused death within 15-20 min, but this could be prevented by pretreating mice with PAF-receptor (PAF-R) antagonists or PAF-acetylhydrolase (PAF-AH). A low dose of LPS (5 mg/kg body wt) did not impair PAF-induced death, whereas higher doses (10 or 20 mg/kg body wt) delayed death, probably via LPS cross-tolerance. Cross-tolerance occurred only when PAF was injected simultaneously with LPS or within 30 min of LPS injection. Tolerance does not appear to be due to an abundant soluble mediator. Histologic examination of lungs and liver and measurement of circulating TNF-α and IL-10 levels suggested that the inflammatory response is not diminished during cross-tolerance. Interestingly, aspirin, a non-specific cyclooxygenase (COX) inhibitor, partially blocked PAF-induced sudden death, whereas NS-398, a specific COX-2 inhibitor, completely protected mice from the lethal effects of PAF. Both COX inhibitors (at 20 mg/kg body wt) independently amplified the cross-tolerance exerted by higher dose of LPS, suggesting that COX-derived eicosanoids may be involved in these events. Thus, PAF does not seem to have a protective role in endotoxemia, but its effects are delayed by LPS in a COX-sensitive way. These findings are likely to shed light on basic aspects of the endotoxin cross-tolerance occurring in many disease conditions and may offer new opportunities for clinical intervention.

Ginkgolide B functions as a determinant constituent of Ginkgolides in alleviating lipopolysaccharide-induced lung injury

Ginkgolides are the major bioactive components of Ginkgo biloba extracts, however, the exact constituents of Ginkgolides contributing to their pharmacological effects remain unknown. Herein, we have determined the anti-inflammatory effects of Ginkgolide B (GB) and Ginkgolides mixture (GM) at equivalent dosages against lipopolysaccharide (LPS)-induced inflammation. RAW 264.7 cell culture model and mouse model of LPS-induced lung injury were used to evaluate in vitro and in vivo effects of GB and GM, respectively. In RAW 264.7 cells, GB and GM at equivalent dosages exhibit an identical capacity to attenuate LPS-induced inducible nitric oxide synthase mRNA and protein expression and subsequent NO production. Likewise, GB and GM possess almost the same potency in attenuating LPS-induced expression and activation of nuclear factor kappa B (p65) and subsequent increases in tumor necrosis factor-α mRNA levels. In LPS-induced pulmonary injury, GB and GM at the equivalent dosages have equal efficiency in attenuating the accumulation of inflammatory cells, including neutrophils, lymphocytes, and macrophages, and in improving the histological damage of lungs. Moreover, GB and GM at equivalent dosages decrease the exudation of plasma protein to the same degree, whereas GM is superior to GB in alleviating myeloperoxidase activities. Finally, though GB and GM at equivalent dosages appear to reduce LPS-induced IL-1β mRNA and protein levels and IL-10 protein levels to the same degree, GM is more potent than GB to attenuate the IL-10 mRNA levels. Taken together, this study demonstrates that GB functions as the determinant constituent of Ginkgolides in alleviating LPS-induced lung injury.

Therapeutic Effects of Bone Marrow-Derived Mesenchymal Stem Cells in Models of Pulmonary and Extrapulmonary Acute Lung Injury

Bone marrow-derived mesenchymal stem cells (MSCs) offer a promising therapy for acute lung injury (ALI). However, whether the same MSC treatments possess similar potential for different ALI models is not fully clear. The present study evaluated the distribution and therapeutic effects of intravenous MSC administration for the treatment of intratracheal lipopolysaccharide (LPS)-induced intrapulmonary ALI and intravenous LPS/zymosan-induced extrapulmonary ALI, matched with lung injury severity, at 30 min and 1, 3, and 7 days. We found that MSC transplantation attenuated lung injury and inhibited lung inflammation in both ALI models. The benefits of MSCs were more significant in the intrapulmonary ALI mice. In vivo and ex vivo fluorescence imaging showed that MSCs primarily homed into the lung. However, more MSCs were recruited into the lungs of the intrapulmonary ALI mice than those of the extrapulmonary ALI mice over the time course. A few MSCs were also detected in the liver and spleen at days 3 and 7. In addition, the two ALI models showed different extrapulmonary organ dysfunction. A lower percentage of cell apoptosis and SDF-1α levels was found in the liver and spleen of the intrapulmonary ALI mice than in those of the extrapulmonary ALI mice. These results suggested that the two ALI models were accompanied with different degrees of extrapulmonary organ damage, which resulted in differences in the trafficking and accumulation of MSCs to the injured lung and consequently accounted for different therapeutic effects of MSCs for lung repair in the two ALI models. These data suggest that intravenous administration of MSCs has a greater potential for the treatment of intrapulmonary ALI than extrapulmonary ALI matched with lung injury severity; these differences were due to more recruitment of MSCs in the lungs of intrapulmonary ALI mice than those of extrapulmonary ALI mice. This finding may contribute to the clinical use of MSCs for the treatment of ALI.

The role of platelet-activating factor receptor (PAFR) in lung pathology during experimental malaria

Malaria-associated lung pathology has been a neglected area in the study of malaria complications. Platelet-activating factor (PAF) is an inflammatory mediator involved in lung inflammation. Using mice lacking the PAF receptor (PAFR(-/-)) we investigated the relevance of signaling through the PAFR for the lung inflammatory process triggered by Plasmodium berghei ANKA (PbA) strain infection. In PAFR(-/-) mice, pulmonary inflammation was markedly reduced as demonstrated by histology, production of certain pro-inflammatory mediators, accumulation of macrophage and CD8+ T cells in the lung parenchyma and the virtual absence of changes in vascular permeability. Therefore, PAFR activation is crucial in the pathogenesis of pulmonary damage associated with PbA infection in C57Bl/6 mice.

Primary graft dysfunction

Primary graft dysfunction (PGD) is the most important cause of early morbidity and mortality following lung transplantation. PGD affects up to 25% of all lung transplant procedures and currently has no proven preventive therapy. Lung transplant recipients who recover from PGD may have impaired long-term function and an increased risk of bronchiolitis obliterans syndrome. This article aims to provide a state-of-the-art review of PGD epidemiology, outcomes, and risk factors, and to summarize current efforts at biomarker development and novel strategies for prevention and treatment.

The value of the lipopolysaccharide-induced acute lung injury model in respiratory medicine

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a syndrome characterized by pulmonary edema and acute inflammation. Lipopolysaccharide (LPS), a major component in Gram-negative bacteria, has been used to induce ALI/ARDS. LPS-induced animal models highlight ways to explore mechanisms of multiple diseases and provide useful information on the discovery of novel biomarkers and drug targets. However, each model has its own merits and drawbacks. The goal of this article is to summarize and evaluate the results of experimental findings in LPS-induced ALI/ARDS, and the possible mechanisms and treatments elucidated. Advantages and disadvantages of such models in pulmonary research and new directions for future investigations are also discussed.

Enhancement of endothelial permeability by coculture with peripheral blood mononuclear cells in the presence of HLA Class II antibody that was associated with transfusion-related acute lung injury

BACKGROUND

HLA Class II antibody-initiated activation of monocytes possessing the corresponding antigen is thought to participate in the pathogenesis of transfusion-related acute lung injury (TRALI). Pulmonary edema, a hallmark of TRALI, is caused by increasing vascular permeability.

STUDY DESIGN AND METHODS

To investigate the contribution of HLA Class II antibody and monocytes to the development of pulmonary edema in TRALI, we studied whether the permeability of human lung microvascular endothelial cells (HMVECs) could be enhanced by coculturing HMVECs with peripheral blood mononuclear cells (PBMNCs) in the presence of HLA Class II antibody-containing plasma, which was implicated in TRALI (anti-HLA-DR plasma). In addition, similar experiments were performed with human umbilical vein endothelial cells (HUVECs). The endothelial permeability to fluoresceinated dextran, which was added from the start of coculture, was measured.

RESULTS

The coculture of HMVECs or HUVECs with PBMNCs in the presence of anti-HLA-DR plasma resulted in the increase of endothelial permeability in the corresponding antigen-antibody-dependent manner. CV-3988, a platelet-activating factor (PAF) receptor antagonist, almost completely suppressed the increase in endothelial permeability. Neutralizing antibodies to tumor necrosis factor (TNF)-α alone and simultaneous addition of the antibodies to TNF-α and interleukin (IL)-1β to the coculture partially suppressed the permeability increase of HMVECs and HUVECs, respectively.

CONCLUSIONS

HLA Class II antibody and monocytes in the corresponding antigen-antibody combination caused the enhancement of endothelial permeability. PAF, TNF-α, and/or IL-1β might be involved in the endothelial permeability increase. HLA Class II antibody-initiated monocyte activation could lead to the development of pulmonary edema in TRALI.

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

Lung ischemia-reperfusion injury remains one of the major complications after cardiac bypass surgery and lung transplantation. Due to its dual blood supply system and the availability of oxygen from alveolar ventilation, the pathogenetic mechanisms of ischemia-reperfusion injury in the lungs are more complicated than in other organs, where loss of blood flow automatically leads to hypoxia. In this review, an extensive overview is given of the molecular and cellular mechanisms that are involved in the pathogenesis of lung ischemia-reperfusion injury and the possible therapeutic strategies to reduce or prevent it. In addition, the roles of neutrophils, alveolar macrophages, cytokines, and chemokines, as well as the alterations in the cell-death related pathways, are described in detail.

Inter-individual variability of plasma PAF-acetylhydrolase activity in ARDS patients and PAFAH genotype

BACKGROUND

Platelet activating factor (PAF), a pro-inflammatory phospholipid, stimulates cytokine secretion from polymorphonuclear leukocytes expressing the transmembrane G-protein coupled PAF receptor. Elevated PAF levels are associated with acute respiratory distress syndrome (ARDS) and sepsis severity. The pro-inflammatory effects of PAF are terminated by PAF acetylhydrolase (PAF-AH).

OBJECTIVE

We sought to determine whether allelic variants in the human PAFAH gene (Arg92His, Ile198Thr, and Ala379Val) contribute to variability in PAF-AH activity in patient plasma obtained within 72 h of ARDS diagnosis.

RESULTS

Plasma PAF-AH activity (mean +/- SD) was higher in patients homozygous for the Arg92 allele compared to His92 allele carriers (2.21 +/- 0.77 vs. 1.64 +/- 0.68 U/min; P < 0.01; n = 31 and 21 respectively). Baseline plasma PAF-AH activity was higher among day 7 survivors vs. day 7 non-survivors (2.05 +/- 0.75 vs. 1.27 +/- 0.63, P = 0.05).

CONCLUSION

These data demonstrate an association between PAF-AH allelic variation, plasma activity, and outcome in ARDS.

Mobilization and margination of bone marrow Gr-1high monocytes during subclinical endotoxemia predisposes the lungs toward acute injury

The specialized role of mouse Gr-1(high) monocytes in local inflammatory reactions has been well documented, but the trafficking and responsiveness of this subset during systemic inflammation and their contribution to sepsis-related organ injury has not been investigated. Using flow cytometry, we studied monocyte subset margination to the pulmonary microcirculation during subclinical endotoxemia in mice and investigated whether marginated monocytes contribute to lung injury in response to further septic stimuli. Subclinical low-dose i.v. LPS induced a rapid (within 2 h), large-scale mobilization of bone marrow Gr-1high monocytes and their prolonged margination to the lungs. With secondary LPS challenge, membrane TNF expression on these premarginated monocytes substantially increased, indicating their functional priming in vivo. Zymosan challenge produced small increases in pulmonary vascular permeability, which were markedly enhanced by the preadministration of low-dose LPS. The LPS-zymosan-induced permeability increases were effectively abrogated by pretreatment (30 min before zymosan challenge) with the platelet-activating factor antagonist WEB 2086 in combination with the phosphatidylcholine-phospholipase C inhibitor D609, suggesting the involvement of platelet-activating factor/ceramide-mediated pathways in this model. Depletion of monocytes (at 18 h after clodronate-liposome treatment) significantly attenuated the LPS-zymosan-induced permeability increase. However, restoration of normal LPS-induced Gr-1high monocyte margination to the lungs (at 48 h after clodronate-liposome treatment) resulted in the loss of this protective effect. These results demonstrate that mobilization and margination of Gr-1high monocytes during subclinical endotoxemia primes the lungs toward further septic stimuli and suggest a central role for this monocyte subset in the development of sepsis-related acute lung injury.

Reducing Ischemia–Reperfusion Injury in Clinical Lung Transplantation

OBJECTIVE

Acute graft dysfunction secondary to ischemia-reperfusion injury (IRI) continues to be the most common cause of early mortality after lung transplantation. The perioperative management with aprotinin could decrease the incidence of severe IRI.

METHODS

A retrospective analysis was conducted of the data from 180 patients who underwent either single lung (56%) or bilateral sequential lung transplantation for similar end-stage lung disease between 1997 and 2005. The most recent 68 patients were managed perioperatively with the high-dose aprotinin infusion regimen (aprotinin group). The ISHLT grade III injury score was used for the diagnosis of severe IRI, which is based on a Pao(2)-FIo(2) ratio of less than 200 mmHg.

RESULTS

Grade III injury was observed in 18% of the patients who were not managed with aprotinin (control group, 152 grafts, 64% single transplants, 68% male, 54 +/- 8 years of age). Early ECMO support was required in 25% of these patients. The associated mortality rate was 40%. Despite significantly longer cold ischemic times (290 +/- 14 minutes vs 231 +/- 14 minutes), older donors (42 +/- 12 years of age), and more frequently observed severely elevated systolic PAP of greater than 60 mmHg (60% vs 48%) as well as more frequently required extracorporeal circulatory support (24%* vs 12%) in the aprotinin group, the incidence of severe IRI (8%) and associated mortality (9%) was markedly reduced.

CONCLUSIONS

The use of aprotinin in LTX surgery, which had strong beneficial effects on patient outcomes, significantly decreased the incidence of severe posttransplant IRI.

Involvement of the platelet-activating factor receptor in host defense against Streptococcus pneumoniae during postinfluenza pneumonia

Although influenza infection alone may lead to pneumonia, secondary bacterial infections are a much more common cause of pneumonia. Streptococcus pneumoniae is the most frequently isolated causative pathogen during postinfluenza pneumonia. Considering that S. pneumoniae utilizes the platelet-activating factor receptor (PAFR) to invade the respiratory epithelium and that the PAFR is upregulated during viral infection, we here used PAFR gene-deficient (PAFR−/−) mice to determine the role of this receptor during postinfluenza pneumococcal pneumonia. Viral clearance was similar in wild-type and PAFR−/− mice, and influenza virus was completely removed from the lungs at the time mice were inoculated with S. pneumoniae ( day 14 after influenza infection). PAFR−/− mice displayed a significantly reduced bacterial outgrowth in their lungs, a diminished dissemination of the infection, and a prolonged survival. Pulmonary levels of IL-10 and KC were significantly lower in PAFR−/− mice, whereas IL-6 and TNF-α were only trendwise lower. These data indicate that the pneumococcus uses the PAFR leading to severe pneumonia in a host previously exposed to influenza A.

PKC-dependent, burn-induced adherens junction reorganization and barrier dysfunction in pulmonary microvascular endothelial cells

Rat lung microvascular endothelial cell monolayers were exposed to donor plasma from burned rats (25% total body surface area) at 1:3 dilution for 30 min. Immunofluorescence analysis revealed that concomitant with gap formation alterations were seen in the adherens junction (AJ) proteins beta-catenin and vascular endothelial-cadherin. Both of these components were shown to exist in a smooth, uniform arrangement at the cell periphery in untreated cells. However, upon exposure to burn plasma, this uniformity was lost, and the AJ proteins showed a disrupted, zipper-like pattern at the cells' edge. In addition, these proteins were absent from areas of gap formation between the cells, and an increase in punctate staining throughout the cells suggests they were internalized in response to burn plasma. Measurements of both transendothelial electrical resistance and FITC-albumin flux across the cell monolayer were used to assess barrier integrity. Our study found that exposure to burn plasma rapidly caused the electrical resistance across confluent monolayers to decrease and albumin flux to increase, phenomena associated with barrier dysfunction. Furthermore, all the above responses to burn plasma were attenuated when cells were pretreated with the PKC inhibitor bisindolylmaleimide, suggesting that PKC is required for burn-induced pulmonary endothelial dysfunction.

PLATELET-ACTIVATING FACTOR RECEPTOR-DEFICIENT MICE SHOW AN UNALTERED CLEARANCE OF NONTYPEABLE HAEMOPHILUS INFLUENZAE FROM THEIR RESPIRATORY TRACT

Platelet-activating factor (PAF), a glycerophospholipid with proinflammatory properties, exerts its biological effects by interacting with the PAF receptor (PAFR) expressed on many different cell types. The PAFR specifically binds phosphorylcholine, the biologically active component of PAF. However, phosphorylcholine is also a component of the cell wall of nontypeable Haemophilus influenzae (NTHi). In recently published in vitro experiments, the invasion of respiratory epithelial cells by NTHi was mediated by the PAFR. To determine the role of the PAFR in host defense against pneumonia induced by NTHi, PAFR-deficient (PAFR-/-) and normal wild-type mice were intranasally inoculated with NTHi. The absence of a functional PAFR was associated with a normal innate immune response as indicated by similar bacterial counts, myeloperoxidase activity, and inflammation within the pulmonary compartment of PAFR-/- and wild-type mice. These data indicate that the PAFR does not interfere with the clearance of NTHi from the respiratory tract.

Cytosolic phospholipase A2-alpha is necessary for platelet-activating factor biosynthesis, efficient neutrophil-mediated bacterial killing, and the innate immune response to pulmonary infection: cPLA2-alpha does not regulate neutrophil NADPH oxidase activity

The role of a cytosolic phospholipase A(2)-alpha (cPLA(2)-alpha) in neutrophil arachidonic acid release, platelet-activating factor (PAF) biosynthesis, NADPH oxidase activation, and bacterial killing in vitro, and the innate immune response to bacterial infection in vivo was examined. cPLA(2)-alpha activity was blocked with the specific cPLA(2)-alpha inhibitor, Pyrrolidine-1 (human cells), or by cPLA(2) -alpha gene disruption (mice). cPLA(2)-alpha inhibition or gene disruption led to complete suppression of neutrophil arachidonate release and PAF biosynthesis but had no effect on neutrophil NADPH oxidase activation, FcgammaII/III or CD11b surface expression, primary or secondary granule secretion, or phagocytosis of Escherichia coli in vitro. In contrast, cPLA(2)-alpha inhibition or gene disruption diminished neutrophil-mediated E. coli killing in vitro, which was partially rescued by exogenous arachidonic acid or PAF but not leukotriene B(4). Following intratracheal inoculation with live E. coli in vivo, pulmonary PAF biosynthesis, inflammatory cell infiltration, and clearance of E. coli were attenuated in cPLA(2)-alpha(-/-) mice compared with wild type littermates. These studies identify a novel role for cPLA(2)-alpha in the regulation of neutrophil-mediated bacterial killing and the innate immune response to bacterial infection.

Thalidomide reduces lipopolysaccharide/zymosan-induced acute lung injury in rats

Pharmacological therapies targeting fulminant lung inflammation in acute lung injury (ALI) need to be improved. We evaluated the effect of thalidomide, a chemical modulating both acute and chronic inflammation, on ALI induced by intravenous administration of lipopolysaccharide (LPS) and zymosan in male Sprague-Dawley rats. Injection of LPS and zymosan induced significant lung inflammation, as evidenced by increased neutrophil sequestration in lung tissue as well as enhanced nitric oxide metabolite (NO(x)(-)) production in the serum and bronchoalveolar lavage (BAL) fluid. Lactate dehydrogenase (LDH) activity and protein concentration in BAL fluid were significantly increased after administration of LPS and zymosan. Pulmonary microvascular permeability was determined using the Evans blue retention method, which showed a significant increase in microvascular permeability after LPS and zymosan administration, indicating the development of ALI. Animals that received thalidomide (100 mg/kg) 2 h prior to LPS injection had significantly reduced pulmonary NO(x)(-) production, pulmonary microvascular permeability, and LDH activity and protein concentration in BAL fluid. We therefore conclude that thalidomide ameliorates lung inflammation and reduces ALI induced by combined LPS and zymosan administration in rats.

Myosin light chain phosphorylation and pulmonary endothelial cell hyperpermeability in burns

Major cutaneous burns result in not only localized tissue damage but broad systemic inflammation causing organ system damage distal to the burn site. It is well recognized that many problems result from the release of inflammatory mediators that target vascular endothelial cells, causing organ dysfunction. The pulmonary microvessels are particularly susceptible to functional abnormalities as a direct consequence of exposure to burn-induced inflammatory mediators. Traditional therapeutic intervention is quite often ineffective in treating burn patients suffering from systemic problems. A possible explanation for this ineffectiveness may be that because so many mediators are released, supposedly activating numerous signaling cascades that interact with each other, targeting of upstream factors in these cascades on an individual basis becomes futile. Therefore, if an end-point effector responsible for endothelial dysfunction following burn injury could be identified, it may present a target for intervention. In this study, we identified phosphorylation of myosin light chain (MLC) as a required element of burn plasma-induced hyperpermeability across rat lung microvascular endothelial cell monolayers. In addition, pharmacological inhibition of myosin light chain kinase (MLCK) and Rho kinase as well as transfection of MLCK-inhibiting peptide blocked actin stress fiber formation and MLC phosphorylation in response to burn plasma. The results suggest that blocking MLC phosphorylation may provide therapeutic intervention in burn patients with the goal of alleviating systemic inflammation-induced endothelial dysfunction.

PAF-mediated pulmonary edema: a new role for acid sphingomyelinase and ceramide

Platelet-activating factor (PAF) induces pulmonary edema and has a key role in acute lung injury (ALI). Here we show that PAF induces pulmonary edema through two mechanisms: acid sphingomyelinase (ASM)-dependent production of ceramide, and activation of the cyclooxygenase pathway. Agents that interfere with PAF-induced ceramide synthesis, such as steroids or the xanthogenate D609, attenuate pulmonary edema formation induced by PAF, endotoxin or acid instillation. Our results identify acid sphingomyelinase and ceramide as possible therapeutic targets in acute lung injury.

Endotoxins stimulate neutrophil adhesion followed by synthesis and release of platelet-activating factor in microparticles

Lipopolysaccharides and triacyl-cysteine-modified proteins of Gram-negative and positive organisms are potent endotoxins. Animal models show that the receptor for platelet-activating factor (PAF) is responsible for many of the deleterious effects of endotoxin, where regulated, localized PAF production localizes the inflammatory response. In contrast, biologically active analogs of PAF (PAF-like lipids) are generated by oxidative attack on phospholipids by chemical reactions that are unregulated and unlocalized. The identity and distribution of the PAF receptor ligand in endotoxemia is unknown. We found human polymorphonuclear leukocytes (PMNs) were a significant source of PAF receptor agonists after stimulation by either class of endotoxin. Production of PAF receptor agonists required that the PMN adhere to a surface, and adhesion (and therefore accumulation of PAF-like bioactivity) in response to endotoxic stimulation was delayed for several minutes. PAF-like oxidized phospholipids were found by mass spectroscopy, but biosynthetic PAF accounted for most of the phospholipid agonists arising from endotoxic stimulation. A significant portion of the PAF made by PMNs was secreted, in contrast to its near complete retention by other inflammatory cells. Endotoxic stimulation induced a respiratory burst with the production of superoxide and the formation and shedding of microparticles. Free and microparticle-bound PAF appeared in the media, and blocking microvesiculation with calpeptin blocked PAF release. The released material activated platelets, and platelets co-aggregated with endotoxin-stimulated PMNs. Adherent PMNs therefore behave differently than suspended cells and are a significant source of free PAF after endotoxin exposure. Leukocytes can couple endotoxic challenge to the widespread circulatory and inflammatory effects of endotoxin.

Regulation of platelet-activating factor synthesis in human monocytes by dipalmitoyl phosphatidylcholine

Platelet-activating factor (PAF) has a major role in inflammatory responses within the lung. This study investigates the effect of pulmonary surfactant on the synthesis of PAF in human monocytic cells. The pulmonary surfactant preparation Curosurf significantly inhibited lipopolysaccharide (LPS)-stimulated PAF biosynthesis (P<0.01) in a human monocytic cell line, Mono mac-6 (MM6), as determined by (3)H PAF scintillation-proximity assay. The inhibitory properties of surfactant were determined to be associated, at least in part, with the 1,2-dipalmitoyl phosphatidylcholine (DPPC) component of surfactant. DPPC alone also inhibited LPS-stimulated PAF biosynthesis in human peripheral blood monocytes. DPPC treatment did not affect LPS-stimulated phospholipase A(2) activity in MM6 cell lysates. However, DPPC significantly inhibited LPS-stimulated coenzyme A (CoA)-independent transacylase and acetyl CoA:lyso-PAF acetyltransferase activity. DPPC treatment of MM6 cells decreased plasma membrane fluidity as demonstrated by electron paramagnetic resonance spectroscopy coupled with spin labeling. Taken together, these findings indicate that pulmonary surfactant, particularly the DPPC component, can inhibit LPS-stimulated PAF production via perturbation of the cell membrane, which inhibits the activity of specific membrane-associated enzymes involved in PAF biosynthesis.

Role of PAF receptors during intestinal ischemia and reperfusion injury. A comparative study between PAF receptor-deficient mice and PAF receptor antagonist treatment

1 The reperfusion of ischemic tissues may be associated with local and systemic inflammation that prevents the full benefit of blood flow restoration. The present study aimed to confirm a role for platelet-activating factor receptor(s) (PAFR) during ischemia and reperfusion injury by using genetically modified mice deficient in the PAFR (PAFR(-/-) mice) and to evaluate comparatively the effectiveness of pharmacological treatment using the PAFR antagonist UK-74,505 (modipafant). 2 The reperfusion of the ischemic superior mesenteric artery (SMA) induced marked local (intestine) and remote (lungs) tissue injury, as assessed by the increase in vascular permeability, neutrophil influx and intestinal hemorrhage and in the production of TNF-alpha. There was also a systemic inflammatory response, as shown by the increase in serum TNF-alpha concentrations and marked reperfusion-associated lethality. 3 After reperfusion of the ischemic SMA, PAFR(-/-) mice had little tissue or systemic inflammation and lethality was delayed, but not prevented, in these mice. Interestingly, the reperfusion-associated increases in tissue concentrations of IL-10 were significantly greater in PAFR(-/-) than wild-type mice. 4 Pretreatment with PAFR antagonist UK-74,505 (1 mg kg(-1)) markedly prevented tissue injury, as assessed by the increase in vascular permeability, neutrophil accumulation, hemorrhage and TNF-alpha concentrations in the intestine and lungs. In contrast, UK-74,505 failed to affect reperfusion-associated lethality and increases in serum TNF-alpha when used at 1 mg kg(-1). 5 Reperfusion-associated lethality and increase in serum TNF-alpha were only affected when a supra-maximal dose of the antagonist was used (10 mg kg(-1)). At this dose, UK-74,505 also induced a marked enhancement of reperfusion-associated increases in tissue concentrations of IL-10. However, at the same dose, UK-74,505 failed to prevent reperfusion-associated lethality in PAFR(-/-) mice any further. 6 The present studies using genetically modified animals and a receptor antagonist firmly establish a role of PAFR activation for the local, remote and systemic inflammatory injury and lethality which follows reperfusion of the ischemic SMA in mice. Moreover, it is suggested that high doses of PAFR antagonists need to be used if the real efficacy of these compounds is to be tested clinically.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

A critical role of leukotriene B4 in neutrophil migration to infectious focus in cecal ligaton and puncture sepsis

Neutrophil migration to an infectious focus is essential for control and resolution of infection. Early studies demonstrated that the failure of such migration is observed in lethal sepsis induced by cecal ligation and puncture (L-CLP), whereas intense neutrophil migration is seen in sublethal CLP (SL-CLP). In this study, we found that inhibition of synthesis of prostaglandins or leukotriene B4 (LTB4) did not modify the failure of neutrophil migration or the survival rate of L-CLP mice. In addition, pretreatment of L-CLP mice with a platelet activating factor (PAF) receptor antagonist (UK74505), despite not interfering with the failure process, significantly increased (33%) the survival rate of the animals. Inhibitors of prostaglandin synthesis (indomethacin and meloxican) and UK74505 did not modify the neutrophil migration observed in SL-CLP. On the other hand, the blockade of LTB4 synthesis (MK886, a 5-lipoxygenase-activating protein inhibitor) or of its receptors (CP-105,696) resulted in reduced neutrophil migration to the peritoneal cavity in SL-CLP mice (62% and 60%, respectively), a consequent increase in the number of bacteria in the inflammatory focus, and a reduced survival rate of the animals (43% and 38%, respectively). Both SL-CLP and L-CLP animals presented significant levels of LTB4 in the peritoneal exudate (3- and 8-fold higher than sham group, respectively) and these were reduced by the pretreatment of mice with LTB4 inhibitors. In conclusion, our results suggest that LTB4, but not prostaglandins or PAF, is an important chemoattractant involved in neutrophil recruitment to infection sites in SL-CLP, a crucial event in confining the invading pathogens to a restricted area. However, in circumstances in which the infection turns to a lethal sepsis, LTB4 is not involved in the observed failure of neutrophil migration to the infectious focus.

Divergent mechanisms of action of the inflammatory cytokines interleukin 1-beta and tumour necrosis factor-alpha in mouse cremasteric venules

1. Protein synthesis dependency and the role of endogenously generated platelet activating factor (PAF) and leukotriene B(4) (LTB(4)) in leukocyte migration through interleukin-1beta (IL-1beta)- and tumour necrosis factor-alpha (TNFalpha)-stimulated mouse cremasteric venules was investigated using established pharmacological interventions and the technique of intravital microscopy. 2. Based on previously obtained dose-response data, 30 ng rmIL-1beta and 300 ng rmTNFalpha were injected intrascrotally (4 h test period) to induce comparable levels of leukocyte firm adhesion and transmigration in mouse cremasteric venules. 3. Co-injection of the mRNA synthesis inhibitor, actinomycin D (0.2 mg kg(-1)), with the cytokines significantly inhibited firm adhesion (49+/-13.6%) and transmigration (67.2+/-4.2%) induced by IL-1beta, but not TNFalpha. 4. In vitro, TNFalpha (1-100 ng ml(-1)), but not IL-1beta, stimulated L-selectin shedding and increased beta(2) integrin expression on mouse neutrophils, as quantified by flow cytometry. 5. The PAF receptor antagonist, UK-74,505 (modipafant, 0.5 mg kg(-1), i.v.), had no effect on adhesion induced by either cytokine, but significantly inhibited transmigration induced by IL-1beta (66.5+/-4.5%). 6. The LTB(4) receptor antagonist, CP-105,696 (100 mg kg(-1), p.o.), significantly inhibited both IL-1beta induced adhesion (81.4+/-15.2%) and transmigration (58.7+/-7.2%), but had no effect on responses elicited by TNFalpha. Combined administration of the two antagonists had no enhanced inhibitory effects on responses induced by either cytokine. 7. The data indicate that firm adhesion and transmigration in mouse cremasteric venules stimulated by IL-1beta, but not TNFalpha, is protein synthesis dependent and mediated by endogenous generation of PAF and LTB(4). Additionally, TNFalpha but not IL-1beta, can directly stimulate mouse neutrophils in vitro. The findings provide further evidence to suggest divergent mechanisms of actions of IL-1beta and TNFalpha, two cytokines often considered to act via common molecular/cellular pathways.

Role of the platelet-activating factor (PAF) receptor during pulmonary infection with gram negative bacteria

The lipid mediator PAF plays an important role in the phagocytosis of particles, including bacteria, and consequent production of pro-inflammatory cytokines, such as TNF-alpha and IL-8. Using a PAF receptor antagonist (UK-74,505) and PAF receptor knock-out mice, we have investigated the relevance of PAF for the inflammatory changes and lethality after pulmonary infection with the gram-negative bacteria Klebsiella pneumoniae in mice. At an inoculum of 3 x 10(6) bacteria, there was marked pulmonary (bronchoalveolar lavage and lung) neutrophilia that started early (2.5 h after infection) and peaked at 48 h. All animals were dead by day 4 of infection. The chemokine KC and the pro-inflammatory cytokine TNF-alpha increased rapidly and persisted for 48 h in the lungs. Pretreatment with UK-74,505 (30 mg kg(-1) per day, p.o.) had no significant effects on the number of infiltrating neutrophils in BAL fluid or lung tissue, as assessed by histology and measuring myeloperoxidase, or on the concentrations of KC. In contrast, concentrations of TNF-alpha and the number of bacteria inside neutrophils were significantly diminished. In order to support a role for the PAF during K. pneumoniae infection, experiments were also carried out in PAFR-deficient mice. In the latter animals, lethality occurred earlier than in wild-type controls. This was associated with greater number of bacteria in lung tissue and diminished percentage of neutrophils containing bacteria in their cytoplasm. Our results suggest that PAF, acting on its receptor, plays a protective role during infection with K. pneumoniae in mice.

Platelet-activating factor drives eotaxin production in an allergic pleurisy in mice

1. The activation of eosinophils via G-protein-coupled seven transmembrane receptors play a necessary role in the recruitment of these cells into tissue. The present study investigates a role for PAF in driving eotaxin production and eosinophil recruitment in an allergic pleurisy model in mice. 2. The intrapleural injection of increasing doses of PAF (10(-11) to 10(-9) moles per cavity) induced a dose- and PAF receptor-dependent recruitment of eosinophils 48 h after stimulation. 3. Intrapleural injection of PAF induced the rapid (within 1 h) release of eotaxin into the pleural cavity of mice and an anti-eotaxin antibody effectively inhibited PAF-induced recruitment of eosinophils. 4. Eosinophil recruitment in the allergic pleurisy was markedly inhibited by the PAF receptor antagonist UK-74,505 (modipafant, 1 mg kg(-1)). Moreover, recruitment of eosinophils in sensitized and challenged PAF receptor-deficient animals was lower than that observed in wild-type animals. 5. Blockade of PAF receptors with UK-74,505 suppressed by 85% the release of eotaxin in the allergic pleurisy. 6. Finally, the injection of a sub-threshold dose of PAF and eotaxin cooperated to induce eosinophil recruitment in vivo. 7. In conclusion, the production of PAF in an allergic reaction could function in multiple ways to facilitate the recruitment of eosinophils -- by facilitating eotaxin release and by cooperating with eotaxin to induce greater recruitment of eosinophils.

Modified endotoxin responses in rats pretreated with 1-->3-beta-glucan (zymosan A)

The present study investigates whether 1-->3-beta-glucans (zymosan particles) modify the pulmonary response of rats to endotoxin (lipopolysaccharide, LPS). Initial experiments were conducted to establish appropriate doses of LPS and regimens for exposure to zymosan and LPS. Interaction between zymosan and LPS exposures was determined to be the deviation from the sum of the individual effects of these agents. Treatment with zymosan on Day 1 and LPS on Day 2 modified several indices of pulmonary responsiveness, including tumor necrosis factor-alpha, albumin, and lactate dehydrogenase activity (LDH) in first acellular lavage fluid as well as the levels of chemiluminescence (CL), NO-dependent CL, and nitric oxide production in cultured lavaged alveolar macrophage cells determined 1 day after exposure. No significant deviation from additivity was found for breathing rate increase and polymorphonuclear leukocytes infiltration. Simultaneous administration of zymosan and LPS or administration of LPS before zymosan did not change these indices of pulmonary responsiveness. These data suggest that the inhibitory effect of 1-->3-beta-glucans on pulmonary responsiveness to endotoxin exposure was apparent only when rats were pretreated with 1-->3-beta-glucan. These results suggest that complex interaction of components may exist in exposure to organic dusts. Therefore, hazard may not be defined by measuring endotoxin or 1-->3-beta-glucans alone.

Effect of aprotinin on endothelial cell activation

BACKGROUND

Cardiopulmonary bypass surgery is often accompanied by a systemic inflammatory response, which can lead to postoperative complications in high-risk patients. This is mediated in part through a systemic rise in inflammatory cytokine levels and the sequestration of leukocytes within organs. Aprotinin has previously been shown to exert an anti-inflammatory effect by preventing the capacity of leukocytes to transmigrate through vascular endothelium. Here we have focused on whether aprotinin has an effect on endothelial cell activation and adhesion molecule expression in response to tumor necrosis factor-alpha, particularly with reference to whether aprotinin inhibits tumor necrosis factor-stimulated neutrophil transendothelial migration.

METHODS AND RESULTS

Intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin expression was studied in tumor necrosis factor-alpha-activated human umbilical vein endothelial cells in the presence of aprotinin at 200, 800, and 1600 kIU/mL. Aprotinin inhibited tumor necrosis factor-alpha-stimulated expression of intercellular adhesion molecule-1 (P =.019 at 1600 kIU/mL) and vascular cell adhesion molecule-1 (P =.003 at 1600 kIU/mL) but not E-selectin. Similar results were obtained in the dermal microvascular endothelial cell line, HMEC-1, which exhibited diminished intercellular adhesion molecule-1 expression in the presence of aprotinin (P =.040 at 800 kIU/mL and P <.001 at 1600 kIU/mL). Aprotinin also significantly inhibited neutrophil transmigration across tumor necrosis factor-alpha-activated human umbilical vein endothelial cells (P =.046 at 1600 kIU/mL).

CONCLUSIONS

We have demonstrated that aprotinin inhibits intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, but not E-selectin, expression on tumor necrosis factor-alpha-activated endothelial cells and that transendothelial migration by neutrophils is also specifically suppressed under these conditions. Our results indicate that endothelial cells can be specifically targeted by aprotinin, therefore adding to our understanding of the anti-inflammatory mechanism of action of aprotinin during cardiopulmonary bypass.

Impact of PAF antagonist BN 52021 (Ginkolide B) on post-ischemic graft function in clinical lung transplantation

BACKGROUND

Platelet activating factor (PAF) is associated with ischemia/reperfusion injury (I/R) after lung transplantation. Following promising experimental results, this prospective trial investigated the potential effect of PAF antagonist BN 52021 (ginkolide B) on clinical Euro-Collins (EC)-based lung preservation.

METHODS

We analyzed 8 double-lung transplant patients in each of 3 groups. In the low-dose group (LDG), donor lungs were perfused with EC containing 2 mg/kg BN 52021, whereas we used 10 mg/kg in the high-dose group (HDG) and placebo in the control group (CG). Before reperfusing the first lung, we administered intravenously 120 mg BN 52021 (LDG), 600 mg BN 52021 (HDG), or placebo (CG). Hemodynamics in terms of pulmonary arterial pressure, pulmonary vascular resistance and serial determinations of the alveolo-arterial oxygen difference (AaDO(2)) were recorded. We measured blood levels of PAF pre-operatively and post-operatively, after 10 minutes and after 3, 8, 24, 48, and 144 hours.

RESULTS

Within 32 hours, we noted a tendency toward better AaDO(2) in the LDG and the HDG compared with the CG (p > 0.05). We observed a significant improvement of AaDO(2) after 3 hours (HDG, p = 0.033) and 8 hours (LDG, p = 0.024), with poorest values in the CG. The PAF concentrations were lowest in the HDG, with significant deterioration 10 minutes after reperfusion. In contrast, placebo led to higher PAF levels. We measured significantly lower PAF concentrations (HDG vs CG) at 10 minutes and at 6 days post-operatively.

CONCLUSIONS

Use of high-dose PAF antagonist BN 52021 can easily be combined with clinical preservation methods and may help optimize pulmonary function with reduced PAF levels, in the early post-ischemic period.

Effects of the PAF receptor antagonist UK74505 on local and remote reperfusion injuries following ischaemia of the superior mesenteric artery in the rat

The effects of the long lasting and potent PAF receptor antagonist UK74505 were assessed on the local and remote injuries following ischaemia and reperfusion (I/R) of the superior mesenteric artery (SMA) in rats. In a severe model of ischaemia (120 min) and reperfusion (120) injury, in addition to the local and remote increases in vascular permeability and neutrophil accumulation, there was significant tissue haemorrhage, blood neutropenia, systemic hypotension and elevated local and systemic TNF-alpha levels. Post-ischaemic treatment with the selectin blocker fucoidin (10 mg kg(-1)) prevented neutrophil accumulation in tissue and, in consequence, all the local and systemic injuries following severe I/R. Treatment with an optimal dose of UK74505 (1 mg kg(-1)) also reversed local and remote neutrophil accumulation, increases in vascular permeability and intestinal haemorrhage. UK74505 partially inhibited blood neutropenia and reperfusion-induced hypotension. Interestingly, both fucoidin and UK74505 prevented the local, but not systemic, increases of TNF-alpha levels following severe I/R injury, demonstrating an important role of migrating cells for the local production of TNF-alpha. However, the results do not support a role for PAF as an intermediate molecule in the production of systemic TNF-alpha. The beneficial effects of UK74505 and other PAF receptor antagonists in models of I/R injury in animals and the safety of UK74505 use in man warrant further investigations of the use of this drug as preventive measure for I/R injury in humans.

An anti-inflammatory property of aprotinin detected at the level of leukocyte extravasation

BACKGROUND

Aprotinin is a serine protease inhibitor used extensively in cardiac operations to reduce postoperative bleeding. It has also been used in trials aimed at reducing the systemic inflammatory response to cardiopulmonary bypass. It remains unclear whether the anti-inflammatory action of aprotinin is related to its general ability to suppress leukocyte activation or whether aprotinin can exercise effects during the leukocyte-endothelial cell adhesion cascade.

METHODS

We used intravital microscopy to study the 3 main stages of the adhesion cascade (leukocyte rolling, firm adhesion, and extravasation) within the mesenteric microcirculation of rats. This in vivo technique allows leukocyte recruitment to be viewed directly through the transparent mesentery of anesthetized animals.

RESULTS

Aprotinin, given by continuous infusion at a clinically relevant dose, exerted no effect on the rolling or firm adhesion responses toward local chemoattractant N -formyl-methyl-leucyl-phenylalanine but significantly inhibited extravasation of leukocytes (73% at 40 minutes, P =.04) into surrounding tissues. In parallel in vitro experiments, aprotinin (used at 200, 800, and 1600 kIU/mL) dose dependently inhibited neutrophil transmigration through cultured endothelial cells in response to 3 different chemoattractants: N -formyl-methyl-leucyl-phenylalanine (P <.001 at 800 and 1600 kIU/mL), interleukin 8 (P <.05 at 200 kIU/mL and P <.001 at 800 and 1600 kIU/mL), and platelet-activating factor (P <.05 at 1600 kIU/mL).

CONCLUSIONS

Our studies have therefore revealed a novel anti-inflammatory mechanism of aprotinin operating at the level of leukocyte extravasation. These findings may be relevant in the prevention of systemic inflammation after cardiopulmonary bypass through the use of protease inhibitors.

E. coli hemolysin-induced lipid mediator metabolism in alveolar macrophages: impact of eicosapentaenoic acid

Escherichia coli hemolysin (HlyA) is a prototype of a large family of pore-forming proteinaceous exotoxins that have been implicated in the pathogenetic sequelae of severe infection and sepsis, including development of acute lung injury. In the present study in rabbit alveolar macrophages (AMs), subcytolytic concentrations of purified HlyA evoked rapid synthesis of platelet-activating factor, with quantities approaching those in response to maximum calcium ionophore challenge. In parallel, large quantities of leukotriene (LT) B(4) and 5-, 8-, 9-, 12-, and 15-hydroxyeicosatetraenoic acid (HETE) were liberated from HlyA-exposed AMs depending on exogenous arachidonic acid (AA) supply. Coadministration of eicosapentaenoic acid (EPA) dose dependently suppressed generation of the proinflammatory lipoxygenase products LTB(4) and 5-, 8-, 9-, and 12-HETE in parallel with the appearance of the corresponding EPA-derived metabolites LTB(5) and 5-, 8-, 9-, and 12-hydroxyeicosapentaenoic acid (HEPE). At equimolar concentrations, EPA turned out to be the preferred substrate over AA for these AM lipoxygenase pathways, with the sum of LTB(5) and 5-, 8-, 9-, and 12-HEPE surpassing the sum of LTB(4) and 5-, 8-, 9-, and 12-HETE by >80-fold. In contrast, coadminstration of EPA did not significantly reduce HlyA-elicited generation of the anti-inflammatory AA lipoxygenase product 15-HETE. We conclude that AMs are sensitive target cells for HlyA attack, resulting in marked proinflammatory lipid mediator synthesis. In the presence of EPA, lipoxygenase product formation is shifted from a pro- to an anti-inflammatory profile.

Lung overexpression of the vascular endothelial growth factor gene induces pulmonary edema

We hypothesized that the angiogenic mediator, vascular endothelial growth factor (VEGF), known to be expressed in the lung and to be capable of inducing local edema in skin, might evoke the development of lung edema if expressed in excess amounts. To test this hypothesis, we developed an in vivo model of VEGF overexpression in the lung on the basis of delivery to the respiratory epithelium of the VEGF165 complementary DNA by an E1(-) adenovirus vector (AdVEGF165). Administration of AdVEGF165 by the intratracheal route (10(9) plaque-forming units [pfu]) to C57Bl/6 mice showed increased expression of VEGF messenger RNA in lung tissue by Northern analysis. Overexpression of VEGF protein in the lung at Days 1 to 10 was confirmed by enzyme-linked immunosorbent assay. Intratracheal administration of AdVEGF165 resulted in a dose-dependent increase in lung wet/dry weight ratios over time, lung histology showed widespread intra- alveolar edema, and pulmonary capillary permeability was significantly increased as quantified by the Evans blue dye assay and [(131)I]albumin permeability. To confirm the specificity of these observations, mice were pretreated with intranasal administration of an adenovirus vector expressing a truncated soluble form of the VEGF receptor flt-1 (Adsflt). Adsflt (10(9) pfu) pretreatment completely abrogated the increased lung wet/dry weight ratio caused by AdVEGF165 administration, whereas an identical adenovirus vector with an irrelevant transgene had no effect upon subsequent AdVEGF165-induced pulmonary edema. Together, these data suggest that overexpression of VEGF in the lung may be one mechanism of increased pulmonary vascular permeability in the early stages of acute lung injury.

Association among filamentous actin content, CD11b expression, and membrane deformability in stimulated and unstimulated bovine neutrophils

OBJECTIVE

To investigate rheologic properties of bovine neutrophils that may result in adhesion molecule-independent sequestration of neutrophils in inflamed lungs of cattle.

ANIMALS

Healthy 2- to 4-week-old male Holstein calves.

PROCEDURES

Neutrophil deformability, filamentous actin (F-actin) content, and CD11b expression was determined for unstimulated bovine neutrophils and bovine neutrophils incubated with the inflammatory mediators tumor necrosis factor-alpha (TNF), platelet-activating factor (PAF), interleukin-8 (IL-8), zymosan-activated plasma (ZAP), Pasteurella haemolytica-derived lipopolysaccharide (LPS), and P haemolytica leukotoxin. Neutrophils were separated into 3 subpopulations on the basis of size. The Factin content and CD11 b expression were evaluated by use of flow cytometry. Leukocyte deformability was evaluated by filtration of dilute whole blood.

RESULTS

The subpopulation of the smallest-sized neutrophils (>90% of neutrophils) contained little F-actin. A subpopulation of slightly larger neutrophils had a profound increase in F-actin content and CD11 b expression. The subpopulation of the largest neutrophils had increased F-actin content and CD11b expression, compared with those for both subpopulations of smaller neutrophils. Incubation of neutrophils with PAF and ZAP but not TNF, IL-8, LPS, or leukotoxin, resulted in decreased neutrophil deformability and increased F-actin content. Incubation with PAF and TNF induced an increase in size of neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

Size can be used to identify subpopulations of large and rigid neutrophils in blood samples from healthy calves. Platelet-activating factor and activated complement fragments are potent inducers of F-actin formation and neutrophil rigidity. Physical changes in neutrophils may impede their transit through lung microvasculature and result in leukocyte trapping independent of adhesion molecule interactions with endothelial cells.

Platelet-activating factor and bacteremia-induced pulmonary hypertension

BACKGROUND

Acute lung injury is a common complication of gram-negative sepsis. Pulmonary hypertension and increased lung vascular permeability are central features of lung injury following experimental bacteremia. Platelet-activating factor is a prominent proinflammatory mediator during bacterial sepsis. Our previous studies have demonstrated that exogenous administration of platelet-activating factor (PAF) induces pulmonary edema without causing pulmonary hypertension. Interestingly, inhibition of PAF activity during Escherichia coli bacteremia prevents the development of both pulmonary hypertension and pulmonary edema. These data suggest that PAF contributes to pulmonary hypertension during sepsis, but that this is unlikely to be a direct vascular effect of PAF. The goal of the present study was to investigate the mechanism by which acute E. coli bacteremia induces pulmonary injury and to define the role that PAF plays in this injury. We hypothesized that the effects of PAF on pulmonary hypertension during bacteremia are due to the effects of PAF on other vascular mediators. Several studies suggest that PAF induces the expression of endothelin-1 (ET), a potent peptide vasoconstrictor. Further, our previous studies have implicated ET as a central mediator of systemic vasoconstriction during bacteremia. We therefore sought to assess whether ET is modulated by PAF. E. coli has also been demonstrated to increase endothelial production of nitric oxide (NO), which contributes to maintenance of basal vascular tone in the pulmonary circulation. We hypothesized that PAF might increase pulmonary vascular resistance during bacteremia by activating neutrophils, increasing expression of ET, and decreasing the tonic release of NO. Furthermore, we hypothesized that hypoxic vasoconstriction did not contribute to pulmonary vasoconstriction during the first 120 min of E. coli bacteremia.

METHODS

Pulmonary artery pressure (PAP), blood pressure (BP), heart rate (HR), and arterial blood gases (ABG) were measured in anesthetized spontaneously breathing adult male Sprague-Dawley rats. E. coli (10(9) CFU/100 g body wt) was injected at t = 0, and hemodynamic data were obtained at 10-min intervals and ABG data at 30-min intervals for a total of 120 min. Sham animals were treated equally but received normal saline in place of E. coli. In treatment groups, a 2.5 mg/kg dose of WEB 2086, a PAF receptor antagonist, was administered intravenously 15 min prior to the onset of sepsis or sham sepsis. The groups were (1) intravenous E. coli (n = 5); (2) intravenous WEB 2086 pretreatment + intravenous E. coli (n = 5); (3) intravenous WEB 2086 alone (n = 5); and (4) intravenous normal saline (n = 6). Nitric oxide metabolites (NOx) and ET concentrations were assayed from arterial serum samples obtained at the end of the protocol. Lung tissue was harvested for measurement of myeloperoxidase (MPO) activity and pulmonary histology.

RESULTS

E. coli bacteremia increased HR, PAP, and respiratory rate early during sepsis (within 20 min), while hypoxemia, hypotension, and hemoconcentration were not manifest until the second hour. Pretreatment with WEB 2086 completely abrogated all of these changes. E. coli bacteremia increased the activity of serum ET, lung MPO, and neutrophil sequestration in the lung parenchyma via a PAF-dependent mechanism. However, the mechanism of increased production of NO appears to be PAF independent.

CONCLUSIONS

These data support the hypothesis that E. coli bacteremia rapidly induces pulmonary hypertension stimulated by PAF and mediated at least in part by endothelin-1 and neutrophil activation and sequestration in the lung. Microvascular injury with leak is also mediated by PAF during E. coli bacteremia, but the time course of resultant hypoxemia and hemoconcentration is slower than that of pulmonary hypertension. The contribution of hypoxic vasoconstriction in exacerbating pulmonary hypertension in gram-negative sepsis is probably a late

Platelet activating factor acetylhydrolase activity in lamb lungs is up-regulated in the immediate newborn period

We recently showed that platelet activating factor (PAF) is an important modulator of pulmonary vasomotor tone in the fetus, with a significant decrease in circulating PAF levels in the immediate newborn period. In this study, we have determined PAF catabolism by PAF acetylhydrolase (PAF-Ah) in lungs of near-term fetal and newborn 2- to 16-h (<1 day) and 6- to 12-day-old lambs. The rate of PAF catabolism by lung homogenate protein from the three groups of lamb lungs was studied at 37 degrees C in 30 mM Tris buffer, pH 7.5, containing 0.01% BSA. Each lung homogenate protein was incubated for 10 min with 50 microM [(3)H]acetyl-PAF at pO(2) <50 Torr (hypoxia) and approximately 100 Torr (normoxia). PAF-Ah activity was quantified as amount of lyso-PAF produced. PAF-Ah activity (means +/- SEM, nmol lyso-PAF/min/mg protein) in fetal lung homogenate was 1.19 +/- 0.14 and 2.46 +/- 0.05 during hypoxia and normoxia, respectively. The corresponding values for the newborns were newborn <1 day, 1.65 +/- 0.26 and 2.95 +/- 0.07 and newborn 6-12 days, 1.25 +/- 0.10 and 2.84 +/- 0.05. In all groups, PAF-Ah activity was higher in normoxia than in hypoxia. During normoxia, PAF-Ah activity in newborn <1 day was significantly higher than the activity in fetus, but similar to the activity in newborn 6- to 12-day-old lamb lungs. These data show a significant up-regulation of PAF-Ah activity in lungs in the immediate newborn period. PAF-Ah gene expression measured by RT-PCR showed a significant up-regulation of the PAF-Ah gene in lungs of lambs <1 day old, suggesting a transcriptional regulation of the PAF-Ah gene in the immediate newborn period. These results suggest that up-regulation of PAF-Ah activity after birth with oxygenation will result in a decrease in circulating PAF levels, thereby facilitating the fall in pulmonary vascular resistance in the immediate newborn period.

Platelet-activating factor (PAF) receptor and genetically engineered PAF receptor mutant mice

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active phospholipid mediator. Although PAF was initially recognized for its potential to induce platelet aggregation and secretion, intense investigations have elucidated potent biological actions of PAF in a broad range of cell types and tissues, many of which also produce the molecule. PAF acts by binding to a unique G-protein-coupled seven transmembrane receptor. PAF receptor is linked to intracellular signal transduction pathways, including turnover of phosphatidylinositol, elevation in intracellular calcium concentration, and activation of kinases, resulting in versatile bioactions. On the basis of numerous pharmacological reports, PAF is thought to have many pathophysiological and physiological functions. Recently advanced molecular technics enable us not only to clone PAF receptor cDNAs and genes, but also generate PAF receptor mutant animals, i.e., PAF receptor-overexpressing mouse and PAF receptor-deficient mouse. These mutant mice gave us a novel and specific approach for identifying the pathophysiological and physiological functions of PAF. This review also describes the phenotypes of these mutant mice and discusses them by referring to previously reported pharmacological and genetical data.

Platelet-activating factor mediates acid-induced lung injury in genetically engineered mice

Adult respiratory distress syndrome (ARDS) is an acute lung injury of high mortality rate, and the molecular mechanisms underlying it are poorly understood. Acid aspiration-induced lung injury is one of the most common causes of ARDS, characterized by an increase in lung permeability, enhanced polymorphonuclear neutrophil (PMN) sequestration, and respiratory failure. Here, we investigated the role of platelet-activating factor (PAF) and the PAF receptor (PAFR) gene in a murine model of acid aspiration-induced lung injury. Overexpression of the PAFR gene in transgenic mice enhanced lung injury, pulmonary edema, and deterioration of gas exchange caused by HCl aspiration. Conversely, mice carrying a targeted disruption of the PAFR gene experienced significantly less acid-induced injury, edema, and respiratory failure. Nevertheless, the efficiency of PMN sequestration in response to acid aspiration was unaffected by differences in PAFR expression level. The current observations suggest that PAF is involved in the pathogenesis of acute lung injury caused by acid aspiration. Thus, inhibition of this pathway might provide a novel therapeutic approach to acute lung injury, for which no specific pharmaceutical agents are currently available.

Priming of the neutrophil respiratory burst is species-dependent and involves MAP kinase activation

BACKGROUND

Priming of the neutrophil respiratory burst has been implicated in the pathogenesis of multi-system organ failure (MSOF) after sepsis and trauma. The intracellular signal transduction pathways that mediate priming are unclear.

METHODS

Human, porcine, rabbit, rat, and mouse neutrophils were assayed by luminol-dependent chemiluminescence in whole blood and purified neutrophil preparations. Multiple priming agents and agonists were studied, as was inhibition of priming by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 and the Mek 1/2 inhibitor PD98059.

RESULTS

Priming by tumor necrosis factor alpha (TNF-alpha), interleukin-8 (IL-8), and granulocyte-macrophage colony-stimulating factor (GM-CSF) was significantly inhibited by SB203580, whereas platelet-activating factor (PAF) priming was unaffected. Neither TNF-alpha nor PAF primed polymorphonuclear neutrophils (PMNs) within whole blood for N-formyl-methionyl-leucyl-phenylalanine (f-MLP) activation, in contrast to activation by complement-opsonized zymosan (OPZ) or low-dose phorbolmyristate acetate (PMA). Both TNF-alpha and PAF, however, primed purified neutrophils for f-MLP activation. In contrast to human and porcine PMNs, rabbit, rat, and mouse PMNs could not be primed by TNF-alpha or PAF, regardless of the final agonist.

CONCLUSIONS

Priming of the PMN respiratory burst proceeds through multiple signaling pathways, depending on the particular priming agent and agonist pair. Differences in priming between PMNs in whole blood and purified preparations may be physiologically significant. There is a pronounced species dependency in the ability to prime the neutrophil respiratory burst.

Molecular basis of the interaction between plasma platelet-activating factor acetylhydrolase and low density lipoprotein

The platelet-activating factor acetylhydrolases are enzymes that were initially characterized by their ability to hydrolyze platelet-activating factor (PAF). In human plasma, PAF acetylhydrolase (EC 3.1.1.47) circulates in a complex with low density lipoproteins (LDL) and high density lipoproteins (HDL). This association defines the physical state of PAF acetylhydrolase, confers a long half-life, and is a major determinant of its catalytic efficiency in vivo. The lipoprotein-associated enzyme accounts for all of the PAF hydrolysis in plasma but only two-thirds of the protein mass. To characterize the enzyme-lipoprotein interaction, we employed site-directed mutagenesis techniques. Two domains within the primary sequence of human PAF acetylhydrolase, tyrosine 205 and residues 115 and 116, were important for its binding to LDL. Mutation or deletion of those sequences prevented the association of the enzyme with lipoproteins. When residues 115 and 116 from human PAF acetylhydrolase were introduced into mouse PAF acetylhydrolase (which normally does not associate with LDL), the mutant mouse PAF acetylhydrolase associated with lipoproteins. To analyze the role of apolipoprotein (apo) B100 in the formation of the PAF acetylhydrolase-LDL complex, we tested the ability of PAF acetylhydrolase to bind to lipoproteins containing truncated forms of apoB. These studies indicated that the carboxyl terminus of apoB plays a key role in the association of PAF acetylhydrolase with LDL. These data on the molecular basis of the PAF acetylhydrolase-LDL association provide a new level of understanding regarding the pathway for the catabolism of PAF in human blood.